1. Field of the Invention
The present invention relates to a source driver integrated chip (IC) for an active matrix electroluminescent display and, more particularly, to a source driver circuit for an active matrix display including a digital-to-analog converter/ramp circuit, in which a digital signal is converted into an analog signal and, at this time, a ramp signal is generated, simultaneously.
2. Discussion of Related Art
Generally, a source driver IC for a flat panel display has been known that provides a data to a panel for one fame time. The source driver IC is the same as a data driver IC or a column driver IC. There are two driving methods of the source driver IC: a passive matrix (PM) and an active matrix (AM). The active matrix comprises a thin film transistor (TFT) serving as a switch in each pixel, and a storage capacitor for storing data. And, it is divided into a voltage driven active matrix and a current driven active matrix. In the case of the voltage driven active matrix, a final output becomes a voltage. On the other hand, the final output becomes a current in the case of the current driven active matrix. It depends on a display device, and an inorganic electroluminescent (EL) is a voltage driven display device.
Hereinafter, a source driver circuit for an active matrix EL display, according to a prior art, will be explained with reference to FIG. 1.
FIG. 1 is a detailed block diagram of a source driver circuit for an active matrix EL display, according to a prior art. The source driver circuit 1 for the active matrix EL display comprises a shift register circuit 10, a data latch circuit 20, a line latch circuit 30, a digital-to-analog converter circuit (voltage type DAC) 40, an analog output buffer circuit 50, and a ramp circuit 60.
The shift register circuit 10 receives a main clock CLK signal and a left/right (L/R) signal for determining a direction, and generates an enable signal that sequentially stores a data in the line latch circuit 30, and the line latch circuit 30 works as a latch for storing the data. The line latch circuit 30 stores the data sequentially by the enable signal of the shift register circuit 10 for one line time, and then, transfers the data stored by a LOAD signal to the digital-to-analog converter circuit (D/A converter circuit) 40 in parallel, at a time. At this time, a new data is stored in the line latch circuit 30.
The D/A converter circuit 40 converts a digital signal into an analog signal and inputs it to the output buffer circuit 50.
In the ramp circuit 60, a reference voltage having a sawtooth waveform should have an excellent linearity, since it has to be equal to the input analog signal. However, it is difficult to obtain the same properties in the ramp circuit 60 and the D/A converter circuit 40 together, since they are separated each other, and thus, a temperature or a threshold voltage changes. The ramp circuit 60 is synchronized to a frame clock and has the sawtooth waveform.
As described above, in the source driver circuit for the active matrix display according to the prior art, an excellent ramp circuit is required to implant full color. Thus, there have been demerits that the high performance ramp circuit has a complex architecture, and the sawtooth waveform having the same property as that of the D/A converter cannot be fabricated due to a change of a temperature or a threshold voltage, since the ramp circuit is separated from the D/A converter circuit.